Using warped spacetime like a magnifying glass, astronomers have caught the most distant signal of its kind from a remote galaxy, and it could open a window into how our universe formed.
The unprecedented radio frequency signal, captured by the Giant MW Radio Telescope (GMRT) in India, came from the galaxy SDSSJ0826+5630, located 8.8 billion light-years from Earth, meaning the signal was emitted when the universe was about a third of its current age.
The signal is an emission line from the most primordial element in the universe: neutral hydrogen. As a result of the big Bang, this element existed throughout the cosmos as a turbulent mist from which the first stars and galaxies eventually formed. Astronomers have long searched for distant signals from neutral hydrogen in the hope of finding the moment when the first stars began to shine, but those signals have proven difficult to detect, given the extraordinary distances involved.
Now, a new study, published December 23 in the journal Monthly Notices of the Royal Astronomical Society, (opens in a new tab) shows that an effect called gravitational lensing could help astronomers detect evidence of neutral hydrogen.
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“A galaxy emits different types of radio signals,” study lead author Arnab Chakraborty (opens in a new tab)cosmologist from McGill University in Canada, said in a statement (opens in a new tab). “Until now, it has only been possible to capture this particular signal from a nearby galaxy, limiting our knowledge to those galaxies closest to Earth.”
The ‘dark ages’ of the universe
Forged approximately 400,000 years after the beginning of the universe, when protons and electrons first joined neutrons, neutral hydrogen populated the dim early cosmos throughout its so-called dark ages, before the first stars and galaxies existed. .
When stars are forming, they emit fierce ultraviolet light that strips electrons from much of the hydrogen. atoms in the space around them, thus ionizing the atoms so that they are no longer neutral. Eventually, the young stars lose their ultraviolet intensity, and some of the ionized atoms recombine into neutral hydrogen. Detecting and studying neutral hydrogen can provide insight into the lives of the first stars, as well as the time before stars existed.
Neutral hydrogen emits light at a characteristic wavelength of 21 centimeters. But using neutral hydrogen signals to study the early universe is a difficult task, since long-wavelength, low-intensity signals often drown out vast cosmic distances. Until now, the farthest 21 cm hydrogen signal detected was 4.4 billion light-years away.
Gravitational lenses are approaching the past
To find a signal at twice the previous distance, the researchers turned to an effect called gravitational lensing.
In his theory of generality relativityAlbert Einstein explained that gravity it is not produced by an invisible force, but rather is our experience of space-time warping and distorting in the presence of matter and energy. Gravitational lensing occurs when a massive object comes between our telescopes and its source. In this case, the space-warping object was the gigantic star-forming galaxy SDSSJ0826+5630, which used its powerful warping effect to act as a lens focusing a faint and distant neutral hydrogen signal for the GMRT.
“In this specific case, the signal is deflected by the presence of another massive body, another galaxy, between the target and the observer,” co-author of the study. nirupam roy, associate professor of physics at the Indian Institute of Sciences, said in the statement. “This effectively results in magnifying the signal by a factor of 30, allowing the telescope to pick it up.”
Now that the researchers have found a way to probe previously unattainable clouds of hydrogen, they want to use it to better map the universe through its various cosmological eras, and hopefully identify the moment when the first stars began to shine.